The invention generally relates to length-changing electromechanical solid state actuators such as an electrostrictive, magnetostrictive or solid-state actuator. In particular, the present invention relates to a compensator assembly for a length-changing actuator, and more particularly to an apparatus and method for degasifying or fluid filling a solid state actuated high-pressure fuel injector for internal combustion engines.
A known solid-state actuator includes a ceramic structure whose axial length can change through the application of an operating voltage or magnetic field. It is believed that in typical applications, the axial length can change by, for example, approximately 0.12%. In a stacked configuration of piezoelectric elements of a solid-state actuator, the change in the axial length is magnified as a function of the number of elements in the actuator. Because of the nature of the solid-state actuator, it is believed that a voltage application results in an instantaneous expansion of the actuator and an instantaneous movement of any structure connected to the actuator. In the field of automotive technology, especially, in internal combustion engines, there is a need for the precise opening and closing of an injector valve element for optimizing the spray and combustion of fuel. Therefore, in internal combustion engines, solid-state actuators are now employed for the precise opening and closing of the injector valve element.
During operation, components of an internal combustion engine experience significant thermal fluctuations that result in the thermal expansion or contraction of the engine components. For example, a fuel injector assembly includes a valve body that may expand during operation due to the heat generated by the engine. Moreover, a valve element operating within the valve body may contract due to contact with relatively cold fuel. If a solid state actuator is used for the opening and closing of an injector valve element, it is believed that the thermal fluctuations can result in valve element movements that can be characterized as an insufficient opening stroke, or an insufficient sealing stroke. It is believed that this is because of the low thermal expansion characteristics of the solid-state actuator as compared to the thermal expansion characteristics of other fuel injector or engine components. For example, it is believed that a difference in thermal expansion of the housing and actuator stack can be more than the stroke of the actuator stack. Therefore, it is believed that any contractions or expansions of a valve element can have a significant effect on fuel injector operation.
It is believed that conventional methods and apparatuses that compensate for thermal changes affecting solid state actuator operation have drawbacks in that they either only approximate the change in length, they only provide one length change compensation for the solid state actuator, or that they only accurately approximate the change in length of the solid state actuator for a narrow range of temperature changes.
It is believed that there is a need to provide thermal compensation that overcomes the drawbacks of conventional methods.
The present invention provides a method of degasifying a fluid of a compensator that compensates for distortion of a fuel injector due to thermal distortion, brinelling, wear and mounting distortion. In particular, the compensator includes a body including a first body end and a second body end extending along a longitudinal axis. The body has a body inner surface facing the longitudinal axis and a fitting, a first piston having a first working surface and a second working surface distal to the first working surface. The first piston includes an extension portion coupled to the first piston. A second piston disposed proximate the extension portion of the first piston and having a spring disposed therebetween. The second piston has a surface that confronts the second working surface, a first sealing member coupled to the second piston, and a flexible fluid barrier coupled to the first piston and the second piston. In a preferred embodiment, the method is achieved by immersing the piston assembly in a container of fluid; and establishing a pressure on the medium acting on the fluid that is lower than ambient air pressure so that a gaseous medium trapped in at least one of the fluid and the piston assembly is generally removed therefrom.
The present invention further provides for a method of filling a compensator that compensates for distortion of a fuel injector due to thermal distortion, brinelling, wear and mounting distortion. The compensator includes a body having a first body end and a second body end extending along a longitudinal axis. The body has a body inner surface facing the longitudinal axis and a fitting, a first piston having a first working surface and a second working surface distal to the first working surface. The first piston includes an extension portion coupled to the first piston. A second piston disposed proximate the first piston. The second piston has a surface that confronts the second working surface, a first sealing member coupled to the second piston, and a flexible fluid barrier. In a preferred embodiment, the method is achieved by providing a gap between the first piston and the second piston by coupling the first piston and second piston to form a piston assembly; immersing the piston assembly in a container containing fluid; and establishing a pressure on the fluid in the container to a predetermined pressure for at least one predetermined time period.